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A nearly 70-year-old procedure, , or BS, continues to gain momentum as a popular approach to combat morbid obesity. The procedure results in dramatic weight loss over a short period of time. However, have reported that about 40% of BS patients develop gallstones after surgery, and these rocklike deposits of bile fluid can cause severe pain when they block a bile duct.

So why do some patients develop gallstones, while others do not?

Jennifer Oosthuizen/Centers for Disease Control and Prevention

Researchers found that Enterobacteriaceae, such as the one shown here, and Lactobacillaceae, were abundant in bariatric surgery patients who did not develop gallstones.

Maimoena S.S. Guman, a researcher at Amsterdam University Medical Centers who already had found that gallstones form differently in BS patients than in the general population, in the Journal of Lipid Research on efforts to answer this question.

“The unique part of this research is that this is the first attempt to investigate protective mechanisms instead of causality for gallstone development,” Guman stated in an email.

To identify baseline differences between BS patients who did and did not develop gallstones, Guman’s team studied 88 patients, analyzing three metrics prior to surgery: the fasting metabolome, the liver and adipose transcriptome, and the gut microbiome. They monitored gallstone development after surgery and analyzed differences in each population for possible protecting factors. In line with previous reports, they found that 32 of the 88 patients, or 36.4%, developed gallstones or sludge (which precedes gallstones) or reported gallstone symptoms within two years of the procedure.

The metabolic analysis showed higher concentrations of plasma metabolites, including a number of conjugated bile acids, in the patients with gallstones. In the same patient group, transcriptomic analysis showed the upregulated expression of 15 genes related to processes including cell division, cholesterol/fatty acid metabolism and tissue inflammation.

In analyzing the gut microbiome, Guman’s team found differentially expressed strains between the patient groups. Four of these strains were enriched in patients with gallstones, includingRuminococcus gnavus, a biomarker for gallstones. Patients who did not develop gallstones, however, had an enrichment in 37 different strains of bacteria, 7 belonging to the Enterobacteriaceae family and 12 to the Lactobacillae family, including a strain used in the making of yogurt: Lactobacillus casei.

When asked if a simple probiotic source, like yogurt, could help protect against gallstone development, Guman wrote, “Based on our results it would be too early to conclude that a simple intervention as having yoghurt enriched with Lactobacillaceae would help, although this finding has been described previously. An intervention study with one group having Lactobacillaceae, either in yoghurt or maybe as supplement pills, would be needed to prove this relationship.”

This study was driven by the desire to gain knowledge that could help protect BS patients from gallstone development. Guman’s team has identified factors that may lead to that goal while opening doors for new avenues of research.

“Prevention is better than cure,” Guman wrote, “but first, we need more research, and I hope this work has inspired others to keep digging further.”